1) Field of the Invention
The present invention relates to a passenger judging apparatus with a load sensor for a judgment on passengers (persons in a vehicle or the like, including a driver), located in a seat or the like. The invention is suitable for use in a safety device from collisions, such as an air bag.
2) Description of the Related Art
For example, for expansion control of an air bag, since it is a desirable manner to seize previously the body dimensions, physiques or the like of objects to be protected prior to the control of an expansion mode, a load sensor has so far been built in a seat of a vehicle (or in the vehicle) to make a judgment on the presence or absence of a passenger(s) or the body dimensions thereof on the basis of an output of the built-in load sensor. Basically, on the basis of an output voltage of the load sensor with respect to a predetermined threshold, a judgment is made as to non-seated, adult-seated and child-seated conditions.
However, the output of the load sensor varies with the getting-in/out of a passenger, posture variation thereof, variation of gravity acceleration (G) applied to the passenger during running (which will be referred to hereinafter as “running G”), and others, and in the case of a fixed threshold type, an erroneous judgment output occurs temporarily due to the variation of the output of the load sensor stemming therefrom.
For this reason, for the passenger judgment, it needs that a careful judgment operation is conducted to eliminate the temporary erroneous judgment output stemming from the posture variation of a passenger, the running G applied to the passenger, or the like for achieving the improvement of the judgment accuracy. Usually, the elimination of such a temporary erroneous judgment output has been made through the use of low-pass filter processing (low-frequency component extraction or averaging processing).
For example, EP99/00407 discloses a technique in which the judgment is made in a manner that an average value of the largest ten data of the past detection data is calculated to compare the resultant average value with a threshold. However, this technique has an advantage of improving the judgment accuracy and, at the same time, has a disadvantage that a delayed judgment result alteration occurs in a situation, such as replacement or getting-in/out of passengers, which requires an alteration of the judgment result.
In addition, Japanese Patent Laid-Open No. (HEI) 10-194079 discloses as technique in which a behavior of a vehicle is detected through the use of a G sensor and, when a decision is made that a vehicle is not in a stable condition, no alteration of the judgment takes place in spite of a change of a passenger detection result. However, this system requires the additional employment of the G sensor and takes no effect with respect to a variation of output of a load sensor in a case in which a passenger spontaneously changes his/her posture regardless of running conditions.
That is, although conventional passenger judgment techniques using an output of a load sensor is effective in providing a judgment result with high accuracy, they require the prolonged time taken for the judgment and, hence, cannot cope with a case in which the necessity for the passenger judgment information arises rapidly, for example, immediately after the getting-in/out of a passenger.